Polyethylene terephthalate polymers (which may be hereinafter referred to as "PET") having ethylene terephthalate units as major structural units have been heretofore widely used for forming molded products such as packaging materials, containers and the like because of their superior properties such as high mechanical strength, transparency, gas barrier property, and hygienic qualities.
However, such PET packaging materials and containers are not always sufficient in gas barrier property against oxygen or other gases, and are unsatisfactory for the drawback of changing the properties of contents in the case of long-term storage, small-size containers or requirement for high gas barrier property. Packaging materials and containers should be essentially transparent to permit inspection of contents and, in such case, should protect the contents against the degradation and the discoloration thereof which occur due to ultraviolet ray irradiation.
For improvements in the gas barrier property of PET packaging materials and containers, it has been proposed to laminate an ethylene-vinyl alcohol copolymer, polyamide resin or other resins which are superior to PET in gas barrier property. However, when a multi-layer structure on PET is stretched, interlaminar separation may occur for a low adhesion of the resins to PET, presumably leading to impairment of gas barrier property. Further because of their low compatibility with PET, these resins of the defective multi-layer molded product can not be reused by mixing with a virgin material to produce a transparent molded product.
A mixture of PET and polyethylene isophthalate or a copolymer thereof was proposed (Japanese Unexamined Patent Publications Nos. 64,624/1984; 64,658/1984; and 315,457/1989). However, a molded product made of the proposed mixture is low in gas barrier property and heat resistance.
A glass tube with a bottom end has been used as a container of high gas barrier property, especially as a reduced pressure blood-collecting tube because it is capable of retaining the reduced pressure for a prolonged time. Yet, since such glass tube is readily damaged and is difficult to handle for its weight, it is currently being replaced by a plastic tube. Nevertheless the plastic reduced pressure blood-collecting tube poses the following problem. The plastic tube has a low gas barrier property compared with the glass tube so that the level of reduced pressure in the tube is decreased with time, and the amount of collected blood is diminished accordingly. For this reason, when a reduced pressure blood-collecting tube is produced, it is necessary to use a resin composition capable of forming a molded product of high gas barrier property.
PET, polyethylene, polypropylene or the like is used as a plastic constituting a reduced pressure blood-collecting bottom-ended tube. Among them, polyethylene is low in transparency and gas barrier property, and is not satisfactory as a plastic constituting a reduced pressure blood-collecting tube. Polypropylene is superior in transparency but inferior in gas barrier property like polyethylene, and is unsatisfactory as a plastic constituting a reduced pressure blood-collecting bottom-ended tube. PET is outstanding in moldability and transparency but low in gas barrier property. Various improvements have been made in the plastics constituting a reduced pressure blood-collecting bottom-ended tube.
For example, Japanese Unexamined Patent Publication No.45,040/1990 proposed a reduced pressure blood-collecting bottom-ended tube made from a mixture of PET and a copolymer of polyethylene isophthalate. However, the proposed tube is defective in the following. 1,3-bis(2-hydroxyethoxy)benzene used as one of the monomers for the copolymer is expensive and is responsible for a high cost of the obtained copolymer. Furthermore, because the copolymer has low impact resistance, the resulting tube is inferior in impact strength, especially drop impact strength. Japanese Unexamined Patent Publication No.22,294/1995 proposed a vacuum blood-collecting tube formed from a mixture of PET with polyester of isophthalic acid, terephthalic acid, 1,3-bis(2-hydroxyethoxy)benzene and ethylene glycol. The proposed tube, however, calls for use of expensive material and is poor in drop impact strength as is the case with the proposal of Japanese Unexamined Patent Publication No.45,040/1990. Hence it is unsatisfactory.